Coleman Furnace 4 Red Flashes (CP9C Echelon Modulating)
Soft lockoutShown as: Four red flashes, two-second pause, repeating
High limit switch open, defective temperature sensor, or the 24 volt fuse is open. Usually an airflow restriction is making the furnace overheat.
Manual wording: “Four Red Flashes - High limit switch open or defective temperature sensor or 24 volt fuse is open. This may be caused by a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow an open fuse on the control board.”
Documented for: CP9C Echelon modulating furnaces
Likely causes, most common first
- Dirty air filter
- Improperly sized duct system
- Faulty blower motor
- Restricted circulating airflow
- Open fuse on the control board
What you can safely check yourself
- Check and replace the air filter
- Open all supply registers and clear the return grille
- Check that the furnace door panel is fully seated
When to call a technician
If the code returns with a clean filter and open vents, have a technician check the blower, ductwork and the board fuse. Never bypass the limit switch.
A Coleman furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installation Manual - Residential Gas Furnace with ECM Motor, Models TP9C*C, YP9C*C, CP9C*C, LP9C*C (Up to 98% Modulating Multi-position), 681292-UIM-B-1211 (Johnson Controls Unitary Products (Coleman), CP9C*C Coleman Echelon modulating gas furnace (manual also covers the identical TP9C, YP9C and LP9C chassis)) · checked 2026-08-25